Plasma or blood serum of humans or animals has a potential risk of being contaminated with viruses. Therefore, the possibility of being infected with high risk viruses such as the AIDS virus and various hepatitis viruses, in the case of humans, cannot be denied, if a blood product manufactured using plasma or serum as a raw material is used.
Methods for preventing viral infection involved in the use of these blood products have been proposed heretofore. For example, a chemical deactivating method using a surfactant or methylene blue has been known as a method for deactivating viruses in blood products. However, any of these methods has problems such as denaturation of proteins, requirements for complicated procedures for removing used chemical substances, and remaining of chemical substances in the finished products.
A method of removing viruses using a membrane, on the other hand, is excellent as compared with the other methods, because this method does not cause proteins to become denatured, is free from a substantial decrease in the activity, and can increase safety of the products against viruses. For example, Japanese Patent Application Laid-open Nos. 016837/1986 and 068176/1988 disclose methods for securing high safety against the hepatitis C virus or AIDS virus by treating plasma with porous hollow fiber having special performance.
Japanese Patent Application Laid-Open Nos. 192368/1989 and 254205/1989 disclose a filtration method and system using a filter membrane made of regenerated cellulose similarly. All these patent applications propose a method for removing viruses on the basis of size exclusion according to their size. On the other hand, Japanese Patent Application Laid-open No. 28581/1998 discloses a method for removing viruses under special conditions of a solution using a membrane having pores with a diameter larger than the size of the viruses.
Focusing attention on the fact that envelope viruses bond with LDL (low density lipoprotein), Japanese Patent Application Laid-open No. 334037/2000 proposes a method for removing the viruses using the membrane for removing LDL.
All these methods, however, have drawbacks. Patent documents 5 and 6 described above employ a method of removing viruses by utilizing exclusion or adsorption according to causing the viruses to aggregate under special conditions or causing them to bond with other mixtures. A problem with this method is the limitation to the type of viruses that can be removed. Another problem is an inconstant removing effect according to fluctuation of conditions.
On the other hand, Japanese Patent Application Laid-open Nos. 16837/1986 and 68176/1988 disclose methods for separating into viruses and proteins which have a smaller diameter than viruses depending on size thereof, the disclosed membranes is not necessarily satisfied about both virus removal ratio and protein permeating performance. Further, although the methods disclosed in Japanese Patent Application Laid-Open Nos. 192368/1989 and 254205/1989 are excellent with respect to viruses removal ratio, these methods cannot be applied in practical use due to the limited amount of proteins that can be treated.